38 MISSISSIPPI EXPERIMENT STATION. 



numerous small clusters of fibrous cells with thickened lignified walls. 

 These resemble ordinary bast fibres except that the lumen is compara- 

 tively wide and the cells large, being about 39^ in diameter, with a wall 

 about 5m in thickness. In the hybrid cortex, there are similar clusters 

 of fibrous cells; here they are sUghtly larger, averaging 50^ in diameter, 

 with a wall thickness about 5^. The clusters are not so abundant, 

 nor are there as many fibers in a cluster, not being more than half as 

 many fibers altogether. In the cortex of the Radish root, these fibers 

 are entirely lacking. In each of the three plants, the ground tissue 

 cells of the cortex become shorter inward and gradually pass over into 

 medullary rays separating the vascular bundles. Between the bundles, 

 they are elongated in the direction of the root radius. In Radish, there 

 are 2-12 rows of cells in each ray; the cells being 15 - 75m long, and 

 15 - 30m wide. In Kohlrabi, there are 3-4 rows of cells in a ray, the 

 cells being 15m wide and 25 - 30m long; in the hybrid, there are 4-8 

 rows of cells in a ray, the cells being 24 - 30m wide, and 40 - 60m long " 

 (figs. 45, 46, and 47). In Radish, and in the hybrid, the rays widen 

 toward the pith, the cells gradually passing over into the large, globular, 

 thin -walled pith cells. Pith cells are lacking altogether in the root of 

 Kohlrabi. 



The phloem areas are rather prominent in each of the three plants, 

 being most prominent in the hybrid. In each, they gradually shade 

 off into the ground parenchyma so it is diffictdt to point out their exact 

 limits. 



The cambium was not sharply differentiated in any of the three 

 plants. 



Cross-sections of Radish roots show xylem strands of varying length 

 and width; they average about 3300m long and 225m wide; in Kohlrabi 

 they average about 200m in width and are 6200m in length, extending 

 from the cortex to the center of the root ; in the hybrid they are of vary- 

 ing widths, ranging from 150 - 550m and are about 12,000m long. The 

 xylem strands in each of the three plants are made up of pitted vessels 

 and tracheids, their walls being more or less lignified. The vessels 

 and tracheids are about the same size in the three plants, being slightly 

 larger in Radish than in the other two; the walls of the tracheid cells 

 in Kohlrabi are about 2.5m thick, and strongly lignified, while the walls 

 of Radish are about 1m thick, and but slightly lignified; in the hybrid 

 the tracheid walls are about 2m in diameter and not strongly lignified. 



Structure op Mid-rib of Leaf: (Studies from cross sections 

 taken near the base of the leaf -blade.) The mid-ribs of the leaves of 

 the three plants have much the same shape and size, and in general, 

 the structure is similar. The mid-rib of Kohlrabi is slightly smaller 

 than the mid-ribs of the other two, being about 4000m in diameter, while 

 in Radish the diameter is about 5500m, and in the hybrid about 5000m. 

 There is about the same number of vascular bundles in each and their 

 distribution is similar in general. In Kohlrabi, the bundles are rather 

 large and compound, each large bundle being composed of 2 to 5 small 

 ones joined more or less; the Radish bundles are not compound as in 

 Kohlrabi, or, if compound, the members are so closely united that they 

 appear as one; these bundles are of rather uniform size, and a"re con- 



